TRACE METAL ANALYSIS OF GYPSUM ASSOCIATED WITH EQUUS SCOTTI FOSSILS FROM WEST TEXAS

Since our last GSA presentation (annual meeting, 2009) additional research has been done on both the vertebrate paleontology and trace metal chemistry of the gypsum mineralization at the Equus scotti West Texas site. Three (3) new E. scotti fossils have been identified, bringing the total to eight (8) E. scotti individuals. What remains striking is the excellent preservation and retained articulation of the horses. All of these fossils have in common gypsum, both as an infused infilling of the hard tissue and permeating the Tule Formation. Some of the gypsum in the Tule, near the E. Scotti burial, consists of massive crystals of 30 cm X 30 cm X 5 cm.

75 % of the fossils are well articulated. Preservation ranges from 90% of the hard tissue in one individual down to 20% in another individual from what we call “Horse Hill”. Six (6) skulls are intact. Examination of teeth indicates two (2) males, three (3) females, and one (1) individual too young to classify. Study of the teeth indicates the ages at burial to be between 4.5 years to approximately 11 years. Additional analysis of the teeth shows the herd to be healthy grass grazers.

The matrix around the fossils consists of gypsum, plus interbedded volcanic ash and clays of the Pleistocene Tule Formation. Trace metal analysis was performed on a gypsum crystal from a vertebrae located in site 7, grid A6. Using standard method SW 6010B the following metals were found, listed from highest to lowest in parts-per-million (PPM): Fe 88.3, Cu 27.1, Al 18.7, Ni 6.25, Ba 3.45, Zn 1.85, Mn 1.70, Mo 0.90, Cr 0.75, and Be 0.05. The following elements were tested for but not found: Pb, Tl, Au, Co, Cd, Ag, and V. As an economic geologist (McQueen) is excited by the Cu. Ni, Ba, Zn, Mo, and Cr values. Could these trace metals be indicative of a mineral deposit nearby? As the one (Drake) who has studied the site’s fossils for nearly 5 years, the possibility of additional research in the area of soft tissue preservation is intriguing.